Piezoelectric material is processed into various piezoelectric elements in accordance with different purposes, particularly, it has been widely used for functional electronic components such as an actuator for generating deformation by applying voltage or a sensor for generating voltage from the deformation of elements in a reverse way, etc.
As the piezoelectric material used for an actuator in the disk drive unit for actuating the fine movements of the slider thereof, a lead (Pb)-based dielectric material having large piezoelectric characteristics, especially, Lead Zirconate Titanate Pb(Zr1-xTix)O3-based perovskite-tpye ferroelectric called as “PZT”, has been widely used, and the piezoelectric material is generally formed by sintering oxide which is formed of individual elements.
Crystal structure of this piezoelectric material formed of PZT varies with the ratio of PbTiO3/PbZrO3. FIG. 1a shows a phase diagram of the PZT. Curie Temperature Tc is a boundary of high-temperature cubic paraelectric phase (Pc) and low-temperature ferroelectric phase. And a morphotropic phase boundary (MPB) divides the ferroelectric phase region into two regions including a tetragonal phase region (FT) and a rhombohedra phase region (FR). As known, when the crystal structure is located at the MPB, the free energy of the spontaneous polarization is quite high, thus this PZT has the best electromechanical conversion property and the best piezoelectric property to obtain an excellent piezoelectric constant d31 or d33.
Moreover, epitaxial grown piezoelectric film has much less crystal defect density therefore is more favorable for the domain alignment. As the result, epitaxial grown piezoelectric film has much larger piezoelectric constant, much less leakage current, and much better thermal stability.
However, it's quite hard to control the composition exactly located at the MPB. Thus a conventional thin film piezoelectric element often applies the composition near the MPB, such as Pb(Zr0.52Ti0.48)O3 or Pb(Zr0.58Ti0.42)O3. As shown in FIG. 1b, the conventional thin film piezoelectric element 100 includes a substrate 101, two electrode layers 102, 103 formed on the substrate 101, and a piezoelectric layer 104 sandwiched between the two electrode layers 102, 103. The layers 102, 103, 104 are typically deposited by sputtering, laser ablation, Sol-gel coating, and various chemical vapor deposition (CVD) or molecular chemical vapor deposition (MOCVD). Concretely, the substrate 101 is made by Si or other materials such as MgO, etc., and the electrode layers 102, 103 are made by Pt, or conductive oxide SrRuO3 (SRO), or their combinations, or other conductive materials. Conventionally, the piezoelectric layer 104 includes composition near the MPB, whose crystal structure is tetragonal phase structure or rhombohedra phase structure. However, the piezoelectric constants of this single-phase piezoelectric element 100 is still inadequate as the product requirement for stroke becomes higher and higher. Furthermore, the single-phase piezoelectric element 100 made by the conventional method has poor thermal stability and the performance is decreased under high temperature condition, and the temperature coefficient factor is high which is not desired by the manufacturers.
Thus, there is a need for an improved thin film piezoelectric element and a manufacturing method to overcome the drawbacks mentioned above.